Coatings are applied to substrates to provide a surface with particular properties such as wear resistance, corrosion resistance, and/or aesthetic appeal. The use of coatings can result in significant cost savings by allowing a substrate to be manufactured from an inexpensive material in a low cost manner while having the surface appearance and surface properties of the coating material. Common uses of coatings include silver plating of dining utensils, chromium plating of automobile trim, ceramic coatings on oil well stringer sections, wear resistant coatings on earth moving equipment, and the coating of metallic wellhead components to improve their heat, pressure, wear, erosion and corrosion resistance. Coatings can also be used to repair surfaces and thereby extend the life of a part.
A variety of different materials having a wide range of structures can be use to coat substrates. Coatings can be applied by a variety of techniques including chemical deposition; electrochemical processes such as electroplating; thermal deposition processes such as sputtering, vapor deposition, flame and plasma spraying; and mechanical coating processes such as dipping, rolling and painting. Coatings having uniform fine microstructure can be applied using techniques such as those discussed in U.S. Pat. No. 4,381,943 of Dickson et al.
The disadvantages of the prior art coating processes are that the coatings frequently are porous, have poor surface quality, contain defects and/or do not adhere well to the substrate. Porosity, poor surface quality and defects have an obvious aesthetic disadvantage, and in addition they may contribute to reduced strength and degradation in the properties of the coating such as the wear and corrosion resistance. If coatings are not well bonded they may spall or flake during thermal cycling, mechanical wear, exposure to chemicals and/or they may flake when the coated parts are deformed. Additionally poor bonding of the coating to the substrate may lead to accelerated and/or preferential corrosion at the coating substrate interface.
After application of a coating using prior art techniques porosity, coating density and bonding may be improved by thermal fusion, sintering, HIP'ing and/or peening. These techniques are costly and if the coating and substrate have different coefficients of thermal expansion rapid or excessive heating or cooling may cause the coating to separate from the substrate.